Methods for electrolytically depositing pretreatment compositions

ABSTRACT

Methods for treating a substrate are disclosed. A method includes contacting a substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal and passing an electric current between an anode and the substrate serving as a cathode to deposit a coating from the pretreatment composition on the substrate. A method for treating an electrically conductive substrate also includes contacting the electrically conductive substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal and electrodepositing a coating on the electrically conductive substrate from the pretreatment composition. A method further includes contacting an electrically conductive substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal; and electrodepositing a coating on the electrically conductive substrate from the pretreatment composition, wherein the coating comprises each of the Group IVB metal and the electropositive metal.

FIELD OF THE INVENTION

The invention relates to the use of electrodeposition to provide coatings on metal substrates.

BACKGROUND OF THE INVENTION

The use of protective coatings on metal substrates for improved corrosion resistance and paint adhesion is common. Conventional techniques for coating such substrates include techniques that involve pretreating the metal substrate with chromium-containing compositions. The use of such chromate-containing compositions, however, imparts environmental and health concerns.

Another popular coating is a phosphate coating (e.g., zinc phosphate). Application of a zinc phosphate coating (a conversion coating) generally requires a surface conditioning of the metal prior to the phosphating step. An example of a surface conditioning step is a rinse in colloidal suspension of a metal salt such as titanium phosphate or dispersions of submicron to micron sized zinc phosphate particles. Following surface conditioning, the metal substrate is exposed to zinc phosphate such as through a bath process. While relatively effective in forming a corrosion-resistant coating on a metal (e.g., a ferrous metal), zinc phosphating processes are generally time consuming, require relatively high temperature processing, and present environmental concerns. Moreover, there are limits on the levels of aluminum that can be treated using zinc phosphate treatments, which represents a challenge given the higher levels of aluminum incorporated into vehicle construction to improve weight savings. As a result, chromate-free and zinc phosphate-free pretreatment compositions have been developed. Such compositions are generally based on chemical mixtures that react with the substrate surface and bind to it to form a protective layer. For example, pretreatment compositions based on a Group IVB metal compound have become more prevalent. Such compositions often contain a source of free fluoride, i.e., fluoride available as isolated ions in the pretreatment composition as opposed to fluoride that is bound to another element, such as the Group IVB metal. Free fluoride can etch the surface of the metal substrate, thereby promoting deposition of a protective coating comprising a Group IVB metal species. Nevertheless, the corrosion resistance capability of these pretreatment compositions has generally been significantly inferior relative to conventional chromium-containing and zinc phosphate-containing pretreatments.

With respect to pretreatment compositions based on zirconium (a Group IVB metal), a coating weight of the zirconium in the protective layer or film is a factor for attaining adequate corrosion protection and paint adhesion. A “coating weight” is the amount or mass of a material in a given coating compared to a certain area. The coating weight can refer to individual elements, individual compounds or a total of all of the elements and/or compounds that comprise a coating. A representative minimum coating weight specification for a zirconium protective layer or film is 20 milligrams per square meter (mg/m²) on a zirconium basis. There have been a number of ways proposed to achieve an acceptable zirconium coating weight. Increasing the concentration in a pretreatment coating bath will often lead to an increase in zirconium coating weight, but at the expense of cost. To maintain a reasonable cost, pretreatment coating baths may limit a concentration of zirconium to a few hundred parts per million (ppm). A second approach is to increase the time of deposition. Process windows and application times, however, may be limited from a few seconds to a few minutes which may not allow sufficient time for a desired coating weight. A third approach is to add accelerators such as copper to the pretreatment coating bath. This approach, however, can result in undesired accelerator (e.g., copper) content in the formed protective layer or film which reduces corrosion resistance. Art has been published that demonstrates the controlled deposition of copper by the use of chelators. In U.S. Pat. No. 9,580,813, the deposited pretreatment coating on the metal substrate should have an average total atomic percent of copper to atomic percent of zirconium that is equal to or less than 1.1. The use of chelating agents is often undesirable because it can increase the difficulty and cost associated with waste water treatment as chelators will prevent or inhibit the precipitation of harmful metal ions (e.g., Ni, Cu, Cr) present in waste water during waste treatment or reclamation. It would be desirable to provide methods for treating a metal substrate that overcome at least some of the previously described drawbacks of the prior art, including the environmental drawbacks associated with the use of chromates and the limitations associated with the use of Group IVB metals such as zirconium. It also would be desirable to provide methods for treating a metal substrate that impart corrosion resistance properties that are equivalent to, or even superior to, the corrosion resistance properties imparted through the use of phosphate- or chromium-containing conversion coatings. It would also be desirable to provide related coated metal substrates.

SUMMARY OF THE INVENTION

The invention is directed to a method for treating a substrate comprising: contacting a substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal; and passing an electric current between an anode and the substrate serving as a cathode to deposit a coating from the pretreatment composition on the substrate.

The invention is also directed to a method for treating an electrically conductive substrate comprising contacting the electrically conductive substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal; and electrodepositing a coating on the electrically conductive substrate from the pretreatment composition.

The invention is further directed to a method for treating an electrically conductive substrate comprising: contacting an electrically conductive substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal; and electrodepositing a coating on the electrically conductive substrate from the pretreatment composition, wherein the coating comprises each of the Group IVB metal and the electropositive metal.

Substrates treated according to the methods of the invention also are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of an electrolytic cell and demonstrates the passage of current to assist in the deposition of a pretreatment layer or film on a substrate;

FIG. 2 shows a side view of a pretreatment apparatus including an anode and substrate 220 connected by a direct current electrical power source and separated by a gasket through which a pretreatment composition is introduced according to Example 2;

FIG. 3 is a graph illustrating the impact of current density on zirconium deposition according to the method described in Example 2. In this figure, Zr CW represents the zirconium coating weight;

FIG. 4 is a graph illustrating the impact of current density on zirconium/copper deposition according to the method described in Example 2. In this figure, Zr CW/Cu CW represents that quotient of the zirconium coating weight and the copper coating weight, both expressed in milligrams per square meter; and

FIG. 5 is an illustration of a Spangler panel used in Example 5.

DETAILED DESCRIPTION

For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers such as those expressing values, amounts, percentages, ranges, subranges and fractions may be read as if prefaced by the word “about,” even if the term does not expressly appear. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Where a closed or open-ended numerical range is described herein, all numbers, values, amounts, percentages, subranges and fractions within or encompassed by the numerical range are to be considered as being specifically included in and belonging to the original disclosure of this application as if these numbers, values, amounts, percentages, subranges and fractions had been explicitly written out in their entirety.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

As used herein, unless indicated otherwise, a plural term can encompass its singular counterpart and vice versa, unless indicated otherwise. For example, although reference is made herein to “a” pretreatment composition, and “an” electropositive metal, a combination (i.e., a plurality) of these components can be used. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.

As used herein, “including,” “containing” and like terms are understood in the context of this application to be synonymous with “comprising” and are therefore open-ended and do not exclude the presence of additional undescribed and/or unrecited elements, materials, ingredients and/or method steps. As used herein, “consisting of” is understood in the context of this application to exclude the presence of any unspecified element, ingredient and/or method step. As used herein, “consisting essentially of” is understood in the context of this application to include the specified elements, materials, ingredients and/or method steps “and those that do not materially affect the basic and novel characteristic(s)” of what is being described.

As used herein, the terms “on,” “upon,” “onto,” “applied on,” “applied onto,” “formed on,” “deposited on,” “deposited onto,” “formed over,” mean formed, overlaid, deposited, and/or provided on but not necessarily in contact with the surface. For example, a coating layer “formed over” a substrate does not preclude the presence of one or more other intervening coating layers of the same or different composition located between the formed coating layer and the substrate.

As used herein, the term “Group IVB metal” refers to an element that is in Group IVB of the Chemical Abstract Service (“CAS”) version of the Periodic Table of the Elements as is shown, for example, in the Handbook of Chemistry and Physics, 63^(rd) edition (1983), corresponding to Group 4 in the actual IUPAC numbering.

As used herein, the term “Group IVB metal compound” refers to compounds that include at least one element that is in Group IVB of the CAS version of the Periodic Table of the Elements.

As used herein, the term “aluminum,” when used in reference to a substrate, refers to substrates made of or comprising aluminum and/or aluminum alloy, and clad aluminum substrates.

As used herein, the term “oxidizing agent,” when used with respect to a component of the pretreatment composition, refers to a chemical which is capable of oxidizing a metal present in the substrate which is contacted by the pretreatment composition. As used herein with respect to “oxidizing agent,” the phrase “capable of oxidizing” means capable of removing electrons from an atom or a molecule present in the substrate or the pretreatment composition, as the case may be, thereby decreasing the number of electrons of such atom or molecule. Therefore, the oxidizing agent is the chemical species which is reduced in the aforementioned electrochemical reaction.

Unless otherwise disclosed herein, as used herein, the terms “total composition weight”, “total weight of a composition” or similar terms refer to the total weight of all ingredients being present in the respective composition including any carriers and solvents.

Unless otherwise disclosed herein, as used herein, the term “substantially free” means that a particular material is not purposefully added to a composition, and, if present at all, only is present in a composition and/or layers comprising the same in a trace amount of 1 parts per million (ppm) or less, based on a total weight of the composition or layer(s), as the case may be. As used herein, unless otherwise disclosed, the term “completely free” means that a particular material is present in a composition and/or layers comprising the same in an amount of 1 parts per billion (ppb) or less, based on a total weight of the composition or layer(s), as the case may be.

As stated above, the invention is directed to a method for treating a substrate comprising, consisting essentially of or consisting of: contacting a substrate with a pretreatment composition comprising, consisting essentially of or consisting of a Group IVB metal and an electropositive metal, wherein the Group IVB metal is in the range of 4 to 40 times an amount of the electropositive metal; and passing an electric current between an anode and the substrate serving as a cathode to form a coating or film including, for example, the Group IVB metal and the electropositive metal from the pretreatment composition on the substrate. The substrate may serve as a cathode in an electrodeposition method with the cathode and a separate anode both being immersed or partially immersed in the pretreatment composition.

The invention is directed to methods for treating a variety of substrates. The substrate may include a portion of a vehicle such as a vehicular body (e.g., without limitation, door, body panel, trunk deck lid, roof panel, hood, roof and/or stringers, rivets, landing gear components, and/or skins used on an aircraft) and/or a vehicular frame. As used herein, “vehicle” or variations thereof includes, but is not limited to, civilian, commercial and military aircraft, and/or land vehicles such as cars, motorcycles, and/or trucks. Examples include but are not limited to substrates such as those that are often used in the assembly of vehicle bodies, vehicle parts and other articles, such as small parts, including fasteners, e.g., nuts, bolts, pins, nails, clips, rivets, buttons and the like. The substrate may be any electrically conductive substrate. One electrically conductive substrate is a metal substrate. Specific examples of metal substrates include, but are not limited to, single element substrates, metal alloy substrates, and/or substrates that have been metallized, such as nickel-plated plastic. According to the invention, the metal or metal alloy can comprise or be steel, aluminum, zinc and/or magnesium. For example, the steel substrate could be cold rolled steel (CRS), hot rolled steel, nickel-flash steel, steel coated with zinc metal, zinc compounds, or zinc alloys, such as electrogalvanized steel, hot-dipped galvanized steel, galvanealed steel, and steel plated with zinc alloy. Also, aluminum alloys (e.g., alloys of the 2XXX, 5XXX, 6XXX or 7XXX), aluminum plated steel and aluminum alloy plated steel substrates may be used. Other suitable non-ferrous metals include copper and magnesium as well as alloys of these materials (e.g., magnesium alloys such as AZ31B, AZ91C, AM60B, ZEK100, or EV31A series). They may also include titanium and/or a titanium alloy. A metal substrate being treated by the pretreatment composition may be a cut edge of a substrate that is otherwise treated and/or coated over the rest of its surface. The metal substrate may be in the form of, for example, a sheet of metal or a fabricated part.

Electrically conductive substrates that may also be suitable for treatment in accordance with the methods of the present invention include electrically conductive polymers and conductive polymeric composites such as carbon fiber reinforced plastics (CFRPs).

A substrate to be treated in accordance with the methods disclosed may first be cleaned to remove grease, dirt, and/or other extraneous matter. At least a portion of the surface of the substrate may be cleaned by physical and/or chemical means, such as mechanically abrading the surface and/or cleaning/degreasing the surface with commercially available alkaline or acidic cleaning agents that are well known to those skilled in the art. Examples of alkaline cleaners suitable for use in the invention include, but are not limited to, Chemkleen™ (CK) 163, 177, 611L, 490MX, 2010LP, SP1, each of which is commercially available from PPG Industries, Inc., and Turco 4215 NC-LT and Ridoline 298, each of which is commercially available from Henkel AG & Co.

Following cleaning of a substrate or substrate surface, the substrate may be rinsed with tap water, deionized water, and/or an aqueous solution of rinsing agents in order to remove any residue. The wet substrate surface may optionally be deoxidized (e.g., an aluminum substrate) or descaled (e.g., a ferrous substrate). The substrate may be dried instead of or prior to deoxidizing/descaling the substrate surface, such as air dried, for example, by using an air knife, by flashing off the water by brief exposure of the substrate to a high temperature or by passing the substrate between squeegee rolls.

At least a portion of the cleaned substrate surface may be deoxidized, mechanically and/or chemically. As used herein, the term “deoxidize” means removal of the oxide layer found on the surface of the substrate in order to promote uniform deposition of the pretreatment composition (described below), as well as to promote the adhesion of the pretreatment composition coating to the substrate surface. Suitable deoxidizers will be familiar to those skilled in the art. A typical mechanical deoxidizer may be uniform roughening of the substrate surface, such as by using a scouring or cleaning pad. Typical chemical deoxidizers include, for example, acid-based deoxidizers such as phosphoric acid, nitric acid, fluoroboric acid, sulfuric acid, chromic acid, hydrofluoric acid, and ammonium bifluoride, or Amchem 7/17 deoxidizers (available from Henkel Technologies, Madison Heights, Mich.), OAKITE DEOXIDIZER LNC (commercially available from Chemetall), TURCO DEOXIDIZER 6 (commercially available from Henkel), or combinations thereof. Often, the chemical deoxidizer comprises a carrier, often an aqueous medium, so that the deoxidizer may be in the form of a solution or dispersion in the carrier, in which case the solution or dispersion may be brought into contact with the substrate by any of a variety of known techniques, such as dipping or immersion, spraying, intermittent spraying, dipping followed by spraying, spraying followed by dipping, brushing, or roll-coating. A skilled artisan will select a temperature range of the solution or dispersion, when applied to the metal substrate, based on etch rates, for example, at a temperature ranging from 50° F. to 150° F. (10° C. to 66° C.), such as from 70° F. to 130° F. (21° C. to 54° C.), such as from 80° F. to 120° F. (27° C. to 49° C.). The contact time may be from five seconds to 10 minutes, such as 15 seconds to five minutes, and such as 30 seconds to three minutes. Descaling typically involves removal of weld scale, light oxides and other impurities from ferrous surfaces. A representative descale product is CORROSOL 888 (commercially available from PPG Industrial Coatings). The substrate may be immersed in a bath of the descale product (e.g., CORROSOL 888) at an elevated temperature on such as from 95° F. to 160° F. (35° C. to 71° C.), such as from 100° F. to 150° F. (38° C. to 66° C.), such as from 105° F. to 145° F. (41° C. to 63° C.), such as from 110° F. to 140° F. (43° C. to 60° C.) for 5 seconds to three minutes.

Following any optional deoxidizing/descaling, the substrate optionally may be rinsed with tap water, deionized water, or an aqueous solution of rinsing agents, and optionally may be dried as described above.

The cleaned and optionally deoxidized/descaled substrate may be contacted by a pretreatment composition in the form of an aqueous solution comprising, consisting essentially of or consisting of a Group IVB metal and an electropositive metal. The method or process to form a coating or film from the pretreatment composition on the substrate is aided by the application of an electric current. In the method or process, an anode and an electrically conductive substrate being treated, serving as a cathode, are placed in an aqueous solution or bath of the pretreatment composition. Upon application of an external bias, the electric current between the cathode and the anode while they are in contact with the pretreatment composition, a layer or film will form on the surface of the substrate from the pretreatment composition. The presence of the electric current to aid or assist a deposition of a layer or a film on a substrate may characterize the method or process as an electrodeposition. A method may be characterized as current-assisted pretreatment (“CAPT”) deposition of a Group IVB metal at the cathode.

The electrodeposition or electrodepositing may include immersing the electroconductive substrate into a bath of an aqueous pretreatment composition, the substrate serving as a cathode in an electrical circuit including the cathode and an anode (e.g., an inert metal such as platinum or a passivated metal such as stainless steel. Sufficient electrical current is applied between the electrodes to aid or assist in a deposition of a layer or film including constituents of the pretreatment composition onto or over at least a portion of the surface of the electroconductive substrate (e.g., aid or assist in a rate of deposition and/or an amount of the Group IVB metal deposited). Such deposition includes, for example, covering at least 75 percent of the substrate surface which was immersed into the pretreatment composition, such as at least 85 percent of the substrate surface, such as at least 95 percent of the substrate surface. Also, it should be understood that as used herein, a pretreatment layer or film or coating formed “over” at least a portion of a “substrate” refers to a composition formed directly on at least a portion of the substrate surface including an entire portion, as well as a composition or coating formed over any coating or pretreatment material which was previously applied to at least a portion of the substrate.

The electrodeposition may be carried out at a current density having an absolute value from |−0.1| milliamperes per square centimeter (mA/cm²) of substrate to |−20| mA/cm² of substrate, such as from |−0.1| mA/cm² of substrate to |−12| mA/cm² of substrate such as from 1-0.31 mA/cm² of substrate to |−2.5| mA/cm² of substrate, such as |−0.35| mA/cm² of substrate to |−1| mA/cm² of substrate, such as less than |−1| mA/cm² of substrate, such as from |−0.1| mA/cm² of substrate to |−1| mA/cm² of substrate, such as |−0.4| mA/cm² of substrate to |−0.8| mA/cm² of substrate, such as |−0.5| mA/cm² of substrate to |−0.7| mA/cm² of substrate such as less than |−0.6| mA/cm² of substrate and such as from |−0.1| mA/cm² of substrate to |−0.6| mA/cm² of substrate. As used herein “absolute value” is denoted by “|X|,” wherein X is a positive or negative number and |+X| is equal to |−X|. In the case of current density, a negative sign indicates a cathodic current density and a positive sign indicates an anodic current density. For example, a current density of |-12| mA/cm² signifies a cathodic current density of −12 mA/cm². One skilled in the art of electrodeposition will understand the amperage and voltage requirements necessary to achieve the disclosed range of current density. A current may be applied under a constantly applied external voltage (e.g., a direct current).

The use of an electric current assists, for example, in a rate of deposition and/or an amount of the Group IVB metal deposited on the substrate particularly in areas of the substrate that are within an electric field produced by the application of an electric current between the electrodes. The acidic nature of the pretreatment composition itself will also foster deposition (passive deposition) on a metal substrate without the electric current or in areas of the substrate that are not directly in contact with the electric field (i.e., the current is negligible or zero). The process described allows for electrical assisted deposition and passive deposition of the Group IVB metal on a substrate.

As mentioned above, the pretreatment composition may include a Group IVB metal and an electropositive metal. The Group IVB metal may, for example, be titanium, zirconium, hafnium or combinations thereof. The Group IVB metal may be introduced to the pretreatment composition as a compound such as an inorganic or organic salt. Suitable compounds of zirconium include, but are not limited to, hexafluorozirconic acid, alkali metal and ammonium salts thereof, ammonium zirconium carbonate, zirconyl nitrate, zirconyl sulfate, zirconium carboxylates and zirconium hydroxy carboxylates, such as zirconium acetate, zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium lactate, ammonium zirconium citrate and mixtures thereof. A suitable compound of hafnium includes, but is not limited to, hafnium nitrate.

As will be appreciated by one skilled in the art, the tendency of chemical species to be reduced is called the reduction potential, is expressed in volts, and is measured relative to the standard hydrogen electrode, which is arbitrarily assigned a reduction potential of zero. The reduction potential for several elements is set forth in Table 1A below (according to the CRC 82^(nd) Edition, 2001-2002). An element or ion is more easily reduced than another element or ion if it has a voltage value, E*, in the following table, that is more positive than the elements orions to which it is being compared.

TABLE 1A Element Reduction half-cell reaction Voltage, E* Potassium K⁺ + e → K −2.93 Calcium Ca²⁺ + 2e → Ca −2.87 Sodium Na⁺ + e → Na −2.71 Magnesium Mg²⁺ + 2e → Mg −2.37 Aluminum Al³⁺ + 3e → Al −1.66 Zinc Zn²⁺ + 2e → Zn −0.76 Chromium (III) Cr³⁺ + 3e → Cr −0.74 Iron Fe²⁺ + 2e → Fe −0.45 Nickel Ni²⁺ + 2e → Ni −0.26 Tin Sn²⁺ + 2e → Sn −0.14 Lead Pb²⁺ + 2e → Pb −0.13 Hydrogen 2H⁺ + 2e → H₂ −0.00 Copper Cu²⁺ + 2e → Cu 0.34 Mercury Hg₂ ²⁺ + 2e → 2Hg 0.80 Silver Ag⁺ + e → Ag 0.80 Gold Au³⁺ + 3e → Au 1.50

Thus, as will be apparent, when the electrically conductive substrate is a metal substrate comprising one of the materials listed earlier, such as cold rolled steel, hot rolled steel, steel coated with zinc metal, zinc compounds, or zinc alloys, hot-dipped galvanized steel, galvanealed steel, steel plated with zinc alloy, aluminum alloys, aluminum plated steel, aluminum alloy plated steel, magnesium and magnesium alloys, suitable electropositive metals for deposition thereon include, for example, nickel, copper, silver, and gold, as well mixtures thereof. These metals will spontaneously deposit on, for example, steel or aluminum alloys given the positive value of the overall electrochemical reaction, as displayed in Table 1B. The term “electropositive metal” refers to metal ions that will be reduced by the metal substrate being treated when the pretreatment solution contacts the surface of the metallic substrate.

TABLE 1B Spontaneous Deposition of Electropositive Metals on Steel Substrate Metal Reduction half- Half-Cell E*_(cell) with steel Ion cell reaction Potential (V) substrate (1) Ni²⁺ Ni²⁺ + 2e → Ni −0.26 V  0.19 V Cu²⁺ Cu²⁺ + 2e → Cu 0.34 V 0.79 V Ag⁺ Ag⁺ + e → Ag 0.80 V 1.25 V Au³⁺ Au³⁺ + 3e → Au 1.50 V 1.95 V (1) E*_(cell) was calculated using the conversion of iron(0) to iron(II) as the oxidation half- cell reaction, which has a value of +0.45 V. This is a surrogate for the oxidation of steel substrate.

When the electropositive metal is or includes copper, both soluble and insoluble compounds may serve as the source of copper in the pretreatment composition. For example, the supplying source of copper ions in the pretreatment composition may be a water-soluble copper compound. Specific examples of such compounds include, but are not limited to, copper sulfate, copper nitrate, copper pyrophosphate, copper thiocyanate, copper bromide, copper oxide, copper hydroxide, copper chloride, copper fluoride, copper fluorosilicate, copper fluoroborate and copper iodate, as well as copper salts of carboxylic acids in the homologous series formic acid to decanoic acid.

The Group IVB metal may be present in the pretreatment composition in an amount that is in the range of 4 to 40 times an amount by weight of the electropositive metal, 5 to 40 times an amount by weight of the electropositive metal or 5.7 to 40 times an amount by weight of the electropositive metal. The Group IVB metal, calculated as elemental metal, may be present in the pretreatment composition in an amount of 100 parts per million (ppm) or more, such as 200 ppm, 250 ppm, 300 ppm, 350 ppm, based on the total weight of the ingredients in the pretreatment composition. The amount of Group IVB metal in the pretreatment composition can range between the recited values inclusive of the recited values.

The electropositive metal may be present in the pretreatment composition in an amount by weight that is in a range of 4 to 40 times less than an amount by weight of the Group IV metal. Examples of an amount of an electropositive metal, calculated as elemental metal, where a Group IVB metal is present in the pretreatment composition in amount by weight of 200 ppm are 5 ppm (40.0 times less), 20 ppm (10.0 times less), 30 ppm (6.7 times less), 35 ppm (5.7 times less), 40 ppm (5.0 times less) and 50 ppm (4.0 times less). The amount of the electropositive metal in the pretreatment composition can range between the recited values inclusive of the recited values.

According to the invention, a source of fluoride may be present in the pretreatment composition. As used herein the amount of fluoride disclosed or reported in the pretreatment composition is referred to as “free fluoride,” that is, fluoride present in the pretreatment composition that is not bound to metal ions or hydrogen ions, as measured in part per millions of fluoride. Free fluoride is defined herein as being able to be measured using, for example, an Orion Dual Star Dual Channel Benchtop Meter equipped with a fluoride ion selective electrode (“ISE”) available from Thermo Fisher Scientific, the sympHony® Fluoride Ion Selective Combination Electrode supplied by VWR International, or similar electrodes. See, e.g., Light and Cappuccino, Determination of fluoride in toothpaste using an ion-selective electrode, J. Chem. Educ., 52:4, 247-250, April 1975. The fluoride ISE may be standardized by immersing the electrode into solutions of known fluoride concentration and recording the reading in millivolts, and then plotting these millivolt readings in a logarithmic graph. The millivolt reading of an unknown sample can then be compared to this calibration graph and the concentration of fluoride determined. Alternatively, the fluoride ISE can be used with a meter that will perform the calibration calculations internally and thus, after calibration, the concentration of the unknown sample can be read directly.

Fluoride ion is a small negative ion with a high charge density, so in aqueous solution it is frequently complexed with metal ions having a high positive charge density or with hydrogen ion. Fluoride anions in solution that are ionically or covalently bound to metal cations or hydrogen ion are defined herein as “bound fluoride.” The fluoride ions thus complexed are not measurable with the fluoride ISE unless the solution they are present in is mixed with an ionic strength adjustment buffer (e.g.: citrate anion or EDTA) that releases the fluoride ions from such complexes. At that point (all of) the fluoride ions are measurable by the fluoride ISE, and the measurement is known as “total fluoride”. The sum of the concentrations of the bound and free fluoride equal the total fluoride, which can be determined as described herein.

The total fluoride in the pretreatment composition can be supplied by hydrofluoric acid, as well as alkali metal and ammonium fluorides or hydrogen fluorides. Additionally, total fluoride in the pretreatment composition may be derived from Group IVB metals present in the pretreatment composition, including, for example, hexafluorozirconic acid or hexafluorotitanic acid. Other complex fluorides, such as fluorosilic acid (H₂SiF₆) or fluoroboric acid (HBF₄), can be added to the pretreatment composition to supply total fluoride. The skilled artisan will understand that the presence of free fluoride in the pretreatment bath can impact pretreatment deposition and etching of the substrate, hence it is critical to measure this bath parameter. The levels of free fluoride will depend on the pH and the addition of chelators into the pretreatment bath and indicates the degree of fluoride association with the metal ions/protons present in the pretreatment bath. For example, pretreatment compositions of identical total fluoride levels can have different free fluoride levels which will be influenced by the pH and chelators present in the pretreatment solution. Accordingly, two distinct pretreatment compositions with the same total fluoride may have different pretreatment deposition properties and in turn different corrosion properties.

According to the invention, the free fluoride of the pretreatment composition may be present in an amount of at least 15 ppm to no more than 2500 ppm, such as 25 ppm to no more than 1000 ppm, such as 50 ppm to no more than 250 ppm with all concentrations based on the total weight of the pretreatment composition. The amount of free fluoride in the pretreatment composition can range between the recited values inclusive of the recited values. As the Group IVB metal is deposited on the substrate during a pretreatment process, the pretreatment composition will see a depletion of the Group IVB metal (e.g., zirconium) and fluorine in the hexafluorozirconic acid, for example, will become free fluoride and a level of free fluoride in the pretreatment composition will, if left unchecked, increase with time as the substrate is pretreated with the pretreatment composition. Accordingly, a metal which forms a fluoride salt having a pK_(sp)) of at least 11 may be added to the bath containing the pretreatment composition, as disclosed at column 6, line 11 to column 7, line 20 in U.S. Pat. No. 8,673,091, which is incorporated herein by reference. pK_(sp) refers to the to the inverse log of the solubility product constant for a compound. For purposes of the invention, the pK_(sp) value for a metal fluoride salt refers to the pK_(sp) values reported in Lange's Handbook of Chemistry, 15th Ed., McGraw-Hill, 1999, Table 8.6. In certain embodiments of the present invention, the metal which forms a fluoride salt having a pK_(sp) of at least 11 is selected from cerium (pK_(sp) of CeF₃ is 15.1), lanthanum (pK_(sp) of LaF₃ is 16.2), scandium (pK_(sp) of ScF₃ is 23.24), yttrium (pK_(sp) of YF₃ is 20.06), or a mixture thereof. Alternatively, or additionally, the depleted Group IVB metal pretreatment composition (e.g., bath) can be replenished (the amount of Group IVB metal in the pretreatment composition can be replenished) using reduced-fluoride Group IVB compositions. These fluoride-deficient Group IVB compositions, in the case of zirconium, can be prepared by mixing hexafluorozirconic acid with either zirconium basic carbonate or zirconyl nitrate in various ratios. By adding these fluoride-deficient compositions to the bath, the level of free fluoride present in the depleted Group IVB bath will be controlled.

The pH of the pretreatment composition may range from 3.0 to 7.0, such as 3.5 to 6.8, such as from 4 to 6, such as from 4 to 5.5, such as from 4 to 5, such as from 4.2 to 6.5, such as from 4.5 to 5.5, such as from 4.5 to 6.0, such as from 4.7 to 5.5, and may be adjusted using, for example, any acid and/or base as is necessary. The pH of the composition may be maintained through the inclusion of an acidic material, including water soluble and/or water dispersible acids, such as hexafluorozirconic acid, nitric acid, sulfuric acid, and/or phosphoric acid. The pH of the composition may be maintained through the inclusion of a basic material, including water soluble and/or water dispersible bases, such as alkali metal hydroxides (e.g., sodium hydroxide, potassium hydroxide), alkali metal carbonates (e.g., sodium carbonate, potassium carbonate), ammonium hydroxide, ammonia, and/or amines such as triethylamine, methylethyl amine, or mixtures thereof.

FIG. 1 shows an illustration of an electrolytic cell and demonstrates the passage of current to assist in the deposition of a pretreatment layer or film on a substrate. Cell 100 includes a volume of pretreatment composition 110 in the form of an aqueous solution. A pretreatment composition in the form of an aqueous solution may be at a temperature ranging from 60° F. to 200° F. (15° C. to 93° C.), such as from 60° F. to 150° F. (15° C. to 65° C.), such as from 60° F. to 125° F. (15° C. to 52° C.), such as from 60° F. to 100° F. (15° C. to 38° C.), such as from 60° F. to 90° F. (15° C. to 32° C.), such as from 70° F. to 180° F. (21° C. to 82° C.), such as from 70° F. to 150° F. (21° C. to 66° C.), such as from 70° F. to 125° F. (21° C. to 52° C.), such as from 70° F. to 100° F. (21° C. to 38° C.), such as from 70° F. to 90° F. (21° C. to 32° C.), such as from 77° F. to 150° F. (25° C. to 66° C.), such as from 77° F. to 125° F. (25° C. to 52° C.), such as from 77° F. to 100° F. (25° C. to 38° C.) and such as from 77° F. to 90° F. (25° C. to 32° C.).

Disposed in pretreatment composition 110 is anode 120 of an inert metal such as platinum or a passivated metal such as stainless steel and substrate 130 that serves as a cathode and on which a pretreatment layer or film is deposited or formed. Direct current electrical power source 140 is connected between anode 120 and substrate 130. A constant voltage (a potential difference) is applied between anode 120 and substrate 130 to drive a decomposition of water in the aqueous solution into oxygen (at the anode) and hydrogen gas (at the cathode). The standard potential difference of the water electrolysis cell (E_(cell)=E_(cathode)−E_(anode)) is −1.23 volts at 25° C. at pH 0 (Std. conc of H+ is 1M). Without wishing to be bound by theory, the electrolysis of water into oxygen and hydrogen is believed to generate hydroxide groups (OH⁻) at an interface of substrate 130 and the pretreatment composition. The generated hydroxide groups react with the Group WB metal ions in the pretreatment composition (e.g., ZrF₆ ²⁻) and form an oxide film or layer on substrate 130 (e.g., a zirconium oxide). Increasing the amount of hydroxide ions at the interface will tend to increase the rate of Group IVB metal oxide film or layer formation (e.g., increase the rate of fluoride and oxide/hydroxide metathesis resulting in zirconium precipitation). A suitable voltage for a pretreatment film or layer formation on substrate 130 is 0.10 to 100 volts, such as 0.50 to 50.00 volts, such as 0.75 to 35.00 volts, such as 1.00 to 20.00 volts. A current density at substrate 130 may be in a range from |−20| milliamps per square centimeter (mA/cm²) such as |−0.1| mA/cm² to |−10| mA/cm², |−0.1| mA/cm² to |−1| mA/cm² and |−0.1| mA/cm² to |−0.6| mA/cm². The current density may be represented as a positive or negative value depending on a direction of the flow of electrons. As described above, a negative sign for current density refers to cathodic deposition.

A thickness of a pretreatment film, layer or coating formed on a substrate such as substrate 130 in FIG. 1 from a pretreatment composition may be less than 1 micrometer, for example, from 10 nanometers to 600 nanometers such as from 20 to 400 nm such as 250 to 300 nm, such as 30 to 250 nm. A coating weight of a Group IVB metal (e.g., zirconium) in a pretreatment layer, coating or film may be 20 mg/m² or greater such as 20 mg/m² to 250 mg/m², such as 25 mg/m² to 200 mg/m², such as 30 mg/m² to 250 mg/m², such as 30 mg/m² to 200 mg/m², such as 40 mg/m² to 250 mg/m², such as 40 mg/m² to 200 mg/m², such as 50 mg/m² to 250 mg/m², such as 50 mg/m² to 200 mg/m², such as 75 mg/m² to 250 mg/m², such as 75 mg/m² to 200 mg/m², such as 100 mg/m² to 250 mg/m², such as 100 mg/m² to 200 mg/m², such as 150 mg/m² to 250 mg/m², such as 150 mg/m² to 200 mg/m², such as 50 mg/m² to 150 mg/m², and such as 75 mg/m² to 150 mg/m². A weight ratio of a Group IVB metal to an electropositive metal in the pretreatment layer, coating or film on a substrate (e.g., a metal substrate) may be greater than 2:1, such as 2.5:1, 3.0:1, 3.5:1, 4:1, 4.5:1, 4.7:1, 5:1, 6:1, 10:1, 15:1 and 20:1. A coating weight of a Group IVB metal on a substrate and a weight ratio of a Group IVB metal to an electropositive metal in the pretreatment layer will depend in part on an immersion time in a pretreatment bath and a current density applied to the bath.

The Group IVB metal deposition rate is a significant factor for ensuring appropriate corrosion protection provided that many industrial processes are limited from a few seconds to a few minutes. As described above, the application of a cathodic bias will increase the rate of Group IVB metal (e.g.: Zirconium) deposition. In this description, deposition rate is defined as the mass of zirconium (Zr), in mg, deposited on a given substrate area (1 m²) normalized over the course of one second. In the present invention, the rate of metal deposition may be at least 0.2 to 2.0 mg Zr per second, such as from 0.2 to 1.8 mg Zr per second, such as from 0.4 to 1.6 mg Zr per second, such as from 0.6 to 1.5 mg Zr per second, such 0.75 to 1.4 mg Zr per second, such as 0.9 to 1.25 mg Zr per second.

Following deposition of a pretreatment layer, coating or film on a substrate from the pretreatment compositions in an electrodepositing pretreatment operation, the substrate may be rinsed with tap water, deionized water, and/or an aqueous solution of rinsing agents in order to remove any residue. Optionally, the substrate may be dried.

A substrate having a pretreatment coating, film or layer thereon (a pretreated substrate) may optionally be further processed to include one or more other coatings, films or layers. One such optional coating, film or layer is a paint. Representatively, the pretreated substrate may be painted using an electrocoat process where the pretreated substrate is placed in a bath containing deionized water and paint solids. Electrodes placed in the bath carry an electric charge that is the same as the paint solids. When an electric charge is applied to the bath, the paint solids are driven away from the electrodes and deposit on the pretreated substrate. Following this electrodeposition process, the painted pretreated substrate may be rinsed and then baked at elevated temperature (e.g., 160° F. (82° C.) to 400° F. (204° C.)) to crosslink and cure the paint on the substrate. On ferric substrates such as cold-rolled steel, scab corrosion creep is typically observed at scribes and cut edges in both accelerated and outdoor exposure corrosion testing. Upon removal from the corrosive environment, filiform corrosion can initiate at the sites of scab corrosion, leading to further cosmetic corrosion failure. Historically, this behavior has been observed even where the substrate had been subjected to either traditional zinc phosphate or next-generation thin film pretreatments. The current-assisted pretreatment of a pretreatment composition including a Group IVB metal and an electropositive metal has shown an ability to suppress or resist filiform corrosion of a substrate (e.g., an iron or aluminum substrate). A pretreatment that suppresses filiform corrosion may be highly desirable—particularly in the automotive OEM sector—as it could prevent further cosmetic corrosion failure from occurring following damage to a coating overlying the pretreated substrate (e.g., chip damage on a vehicle). Additionally, this property of the pretreatment film could facilitate repair of a damaged coating by inhibiting the spread of corrosion from the initial site of coating failure. Still further, current assisted thin film pretreatment of a pretreatment composition including a Group IVB metal and an electropositive metal may extend the service lifetime of automotive or industrial coatings.

According to the invention, a pretreatment film or layer deposited on a substrate may be substantially free, or in some cases may be essentially free, or in some cases may be completely free of phosphate, phosphate ions or phosphate-containing compounds. A pretreatment composition may, in some instances, exclude phosphate ions or phosphate-containing compounds and/or the formation of sludge, such as aluminum phosphate, iron phosphate, and/or zinc phosphate, formed in the case of using a treating agent based on zinc phosphate. As used herein, “phosphate-containing compounds” include compounds containing the element phosphorous such as orthophosphate, pyrophosphate, metaphosphate, tripolyphosphate, organophosphonates, and the like, and can include, but are not limited to, monovalent, divalent, or trivalent cations such as: sodium, potassium, calcium, zinc, nickel, manganese, aluminum and/or iron. When a composition and/or a coating, layer or film including the same is substantially free, essentially free, or completely free of phosphate, this includes phosphate ions or compounds containing phosphate in any form.

Thus, a pretreatment composition and/or coating, layer or film, respectively, deposited from the same may be substantially free, may be essentially free, and/or may be completely free of one or more of any of the elements or compounds listed in the preceding paragraph. A pretreatment composition and/or coating, layer or film deposited from the same that is substantially free of phosphate means that phosphate ions or compounds containing phosphate are not intentionally added, but may be present in trace amounts, such as because of impurities or unavoidable contamination from the environment. In other words, the amount of material is so small that it does not affect the properties of the composition; this may further include that phosphate is not present in the pretreatment composition and/or coating, layer or film deposited from the same in such a level that they cause a burden on the environment. The term “substantially free” means that the pretreatment composition and/or coating, layer or film deposited from the same contain less than 10 parts per million (ppm) of any or all of the phosphate anions or compounds listed in the preceding paragraph, based on total weight of the composition or the layer or film, respectively, if any at all. The term “essentially free” means that the pretreatment composition and/or coating, layer or film including the same contain less than 1 ppm of any or all of the phosphate anions or compounds listed in the preceding paragraph. The term “completely free” means that the pretreatment composition and/or coating, layer of film including the same contain less than 1 parts per billion (ppb) of any or all of the phosphate anions or compounds listed in the preceding paragraph, if any at all.

According to the invention, a pretreatment film or layer deposited on a substrate may exclude chromium or chromium-containing compounds. As used herein, the term “chromium-containing compound” refers to materials that include hexavalent chromium. Non-limiting examples of such materials include chromic acid, chromium trioxide, chromic acid anhydride, dichromate salts, such as ammonium dichromate, sodium dichromate, potassium dichromate, and calcium, barium, magnesium, zinc, cadmium, and strontium dichromate. When a pretreatment composition and/or a coating or a layer, respectively, deposited from the same is substantially free, essentially free, or completely free of chromium, this includes chromium in any form, such as, but not limited to, the hexavalent chromium-containing compounds listed above.

Thus, a pretreatment composition and/or coating, layer or film, respectively, deposited from the same may be substantially free, may be essentially free, and/or may be completely free of one or more of any of the elements or compounds listed in the preceding paragraph. A pretreatment composition and/or coating, layer or film, respectively, deposited from the same that is substantially free of chromium or derivatives thereof means that chromium or derivatives thereof are not intentionally added, but may be present in trace amounts, such as because of impurities or unavoidable contamination from the environment. In other words, the amount of material is so small that it does not affect the properties of the pretreatment composition; in the case of chromium, this may further include that the element or compounds thereof are not present in the pretreatment composition and/or coating, layer or film, respectively, deposited from the same in such a level that it causes a burden on the environment. The term “substantially free” means that the pretreatment composition and/or coating, layer or film, respectively, deposited from the same contain less than 1 ppm of any or all of the elements or compounds listed in the preceding paragraph, based on total weight of the composition or the coating, layer or film, respectively, if any at all. The term “essentially free” means that the pretreatment composition and/or coating, layer or film, respectively, deposited from the same contain less than 0.1 ppm of any or all of the elements or compounds listed in the preceding paragraph, if any at all. The term “completely free” means that the pretreatment composition and/or coating, layer or film, respectively, deposited from the same contain less than 1 parts per billion (ppb) of any or all of the elements or compounds listed in the preceding paragraph, if any at all.

It will be appreciated by those skilled in the art that changes could be made to the aspects described above without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular aspects disclosed, but it is intended to cover modifications which are within the spirit and scope of the disclosed methods, as defined by the appended claims.

EXAMPLES Example 1. Comparison of Corrosion Resistance at Equal Coatings Weights of Zr

Preparation of Zirconium Pretreatment Compositions: Zirconium-containing pretreatment compositions or baths were prepared for testing. Each pretreatment bath was prepared by the addition of a metal-containing species (e.g., hexafluorozirconic acid or potassium hexafluorozirconate for zirconium (Zr) and copper nitrate for copper (Cu) or chromium (III) potassium sulfate for chromium (Cr)) and is described in more detail with each example (copper and trivalent chromium representing electropositive metals relative to the substrate (e.g., cold rolled steel (iron) or aluminum). Zirconium was supplied to the copper-containing pretreatment baths by adding hexafluorozirconic acid (45 wt. % in water) available from Honeywell International, Inc. (Morristown, N.J.); copper was supplied by adding a 2 wt. % Cu solution, which was prepared by dilution of a copper nitrate solution (18 wt. % Cu in water) available from Shepherd Chemical Company (Cincinnati, Ohio). Zirconium was supplied to the chromium-containing pretreatment baths by adding potassium hexafluorozirconate (solid) available from Sigma Aldrich (Milwaukee, Wis.); chromium was supplied by adding chromium (III) potassium sulfate dodecahydrate (solid, >98% purity) available from Sigma Aldrich (Milwaukee, Wis.). After all of the ingredients were added to a pretreatment bath, the bath pH was measured using a pH meter interface (DualStar pH/ISE Dual Channel Benchtop Meter, available from ThermoFisher Scientific, Waltham, Mass., USA; pH probe, Fisher Scientific Accumet pH probe (Ag/AgCl reference electrode)) that was immersed in the pretreatment bath. Free fluoride was measured using a DualStar pH/ISE Dual Channel Benchtop Meter (ThermoFisher Scientific) equipped with a fluoride selective electrode (Orion ISE Fluoride Electrode, solid state, available from ThermoFisher Scientific) by immersing the electrode in the pretreatment solution and allowing the measurement to equilibrate. Then, the pH was adjusted as needed to a specified pH range with Chemfil buffer (an alkaline buffering solution, commercially available from PPG Industries, Inc.) for an increase in pH. For a decrease in pH, hexafluorozirconic acid (45 wt. % in water, available from Honeywell International, Inc., Morristown, N.J.) was used for the copper-containing pretreatment baths. For a decrease in pH for the chromium—containing pretreatment baths, a sulfuric acid solution (approx. 10 wt. % in water prepared from 93%-98% sulfuric acid, available from Alfa Aesar, Tewksbury, Mass.) was used. The free fluoride was adjusted as needed to a range of 25 to 150 ppm with Chemfos AFL (a partially neutralized aqueous ammonium bifluoride solution, commercially available from PPG Industries, Inc. and used according to supplier instructions). The amount of copper in each pretreatment bath was measured using a DR/890 Colorimeter (available from HACH, Loveland, Colo., USA) using an indicator (CuVerl Copper Reagent Powder Pillows, available from HACH). The amount of Zr in the copper-containing pretreatment baths was calculated from the amount of hexafluorozirconic acid added and is reported based on the total weight of the composition. The amount of Cr in the chromium-containing pretreatment baths was calculated from the amount of chromium (III) potassium sulfate dodecahydrate added and is reported based on the total weight of the composition. The amount of Zr in the chromium-containing pretreatment baths was calculated from the amount of potassium hexafluorozirconate added and is reported based on the total weight of the composition.

Preparation of PT Bath A (PT A): PT Bath A was prepared by the addition 18.9 liters of deionized (DI) water to an empty 5-gallon plastic bucket. To the DI water was added hexafluorozirconic acid, and copper nitrate solution. The pH and free fluoride of the bath were adjusted by using Chemfil Buffer and Chemfos AFL, respectively. PT Bath A was applied using an immersion heater on a “low” setting.

Preparation of PT Bath B (PT B): PT Bath B was prepared in a manner analogous to PT Bath A by the addition 18.9 liters of water to an empty five-gallon plastic bucket. To the DI water was added hexafluorozirconic acid and copper solution with the final amount (concentration) of copper in the pretreatment bath being less than in PT Bath A. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively. PT Bath B was applied using an immersion heater on the “low” setting.

Preparation of PT Bath C (PT C): PT Bath C was prepared in a manner analogous to PT Bath A by the addition 18.9 liters of water to an empty five-gallon plastic bucket. To the DI water was added hexafluorozirconic acid and copper solution. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively. This bath was split in five one-gallon aliquots. A single one-gallon aliquot was used for conditions 1C, 1D, 1E, and 1F. The final aliquot was discarded. For the preparation of panels, a single one-gallon aliquot was placed into a plastic cylinder with a magnetic stir bar. The one-gallon bath was stirred at 300 RPM on a magnetic stir plate.

Preparation of PT Bath D (PT D): PT Bath D was prepared in a manner analogous to PT Bath B by the addition 18.9 liters of water to an empty five-gallon plastic bucket. To the DI water was added hexafluorozirconic acid and copper solution. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively. A single one-gallon aliquot was removed and placed into a plastic cylinder with a magnetic stir bar. PT D was stirred at 300 RPM on a magnetic stir plate.

TABLE 2 Group IVB Pretreatment Bath Parameters for Example 1 Pretreatment Free Bath Code Zr (ppm) Cu (ppm) Fluoride (ppm) pH PT A 200 35 90 4.8 PT B 200 5 90 4.8 PT C 200 35 90 4.8 PT D 200 5 90 4.8

Alkaline Cleaner I (AC I): A rectangular, stainless steel tank with a total volume of 37 gallons, equipped with spray nozzles, was filled with 10 gallons of deionized water. To this was added 500 mL of Chemkleen 2010LP (a phosphate-free alkaline cleaner available from PPG Industries, Inc.) and 50 mL of Chemkleen 181ALP (a phosphate-free blended surfactant additive available from PPG Industries, Inc.). Alkaline cleaner I was used for all conditions in Example 1.

Cold rolled steel (CRS) test panels (4″×12″, Item #28110, audit grade, cut only, unpolished) were obtained from ACT Test Panel Technologies (Hillsdale, Mich.). CRS panels were coated using one of three treatment methods, Treatment Methods A, B, or C.

The procedures for Treatment Method A, B, and C are outlined in Tables 3, 4, and 5 below. For panels treated according to Treatment Method A, panels were spray cleaned and degreased for 120 seconds at 10-15 psi in alkaline cleaner IV (125° F.) using Vee-jet nozzles and were then rinsed by immersing in a deionized water bath (75° F.) for 30 seconds followed by a deionized water spray rinse using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (available from Home Depot) for 30 seconds. Panels were then immersed in PT Bath A or PT Bath B for 120 seconds at 80° F. without the application of current. After deposition, the panels were rinsed by a deionized water spray rinse using the using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (75° F.) for 30 seconds and dried with hot air (140° F.) for 120 seconds using a Hi-Velocity handheld blow-dryer made by Oster® (model number 078302-300-000) on high-setting.

For panels treated according to Treatment Method B, panels were cleaned the same manner as in Treatment Method A. The panels were then immersed for the specified time at 80° F. in the specified pretreatment bath. A DC supplied rectifier was used to generate the constant current density of −0.30 mA/cm2 for all of the conditions for Treatment Method B. The rectifier was a Sorensen XG 300-5.6 available from Ameteck located in Berwyn, Pa.). The current assisted pretreatment application conditions were voltage set point of 20V, a ramp time of Os, and pretreatment film thickness was controlled by time modulation with specifics defined in Table 6. The steel panel was the cathode and the anode was a stainless steel panel (3″ by 8″). After pretreatment, the rinsing and drying sequence for Treatment Method B was identical to Treatment Method A.

For panels treated according to Treatment Method C, panels were cleaned the same manner as in Treatment Method A. The panels were then immersed for 480 or 900 seconds at 80° F. in PT Bath D with no current application. After pretreatment, the rinsing and drying sequence for Treatment Method C was identical to Treatment Method A.

TABLE 3 Treatment Method A Step 1A Alkaline cleaner (120 seconds, 125° F., spray application) Step 2A Deionized water rinse (30 seconds, 75° F., immersion application) Step 3A Deionized water rinse (30 seconds, 75° F., spray application) Step 4A Zirconium Pretreatment (120 seconds, 80° F., immersion application) Step 5A Deionized water rinse (30 seconds, 75° F., spray application) Step 6A Hot Air Dry (120 seconds, 140° F.)

TABLE 4 Treatment Method B Step 1B Alkaline cleaner (120 seconds, 125° F., spray application) Step 2B Deionized water rinse (30 seconds, 75° F., immersion application) Step 3B Deionized water rinse (30 seconds, 75° F., spray application) Step 4B Zirconium Pretreatment (cathodic current, 80° F., immersion application) Step 5B Deionized water rinse (30 seconds, 75° F., spray application) Step 6B Hot Air Dry (120 seconds, 140° F.)

TABLE 5 Treatment Method C Step 1C Alkaline cleaner (120 seconds, 125° F., spray application) Step 2C Deionized water rinse (30 seconds, 75° F., immersion application) Step 3C Deionized water rinse (30 seconds, 75° F., spray application) Step 4C Zirconium Pretreatment (variable time, 80° F., immersion application) Step 5C Deionized water rinse (30 seconds, 75° F., spray application) Step 6C Hot Air Dry (120 seconds, 140° F.)

TABLE 6 Treatment conditions for Example 1 Condition Cleaner Pretreatment Application Current Density Immersion Time Treatment Code Bath Composition of Current (mA/cm²) (seconds) Method 1A AC I PT A No — 120 Method A 1B AC I PT B No — 120 Method A 1C AC I PT C No — 480 Method C 1D AC I PT C No — 900 Method C 1E AC I PT C Yes −0.30 60 Method B 1F AC I PT C Yes −0.30 120 Method B 1G AC I PT D Yes −0.30 120 Method B

Following completion of Treatment Methods A, B or C, all panels were electrocoated with ED6107Z (a cathodic electrocoat with components commercially available from PPG as a two component formulation) prepared by mixing 9829 g of E6443 resin blend, 1599 g of E6455Z paste blend, and 7571 g of deionized water. The paint was ultrafiltered removing 25% of the material, which was replenished with 4749 g of deionized water. The film thickness was time-controlled to deposit a target film thickness of 0.6+0.1 mils (15+2 microns) on the pretreated steel panels. The DFT was controlled by changing the amount of charge (coulombs) that passed through the panels. The rectifier (Xantrex Model XFR600-2, Elkhart, Ind., or Sorensen XG 300-5.6, Ameteck, Berwyn, Pa.) was DC power supplied. The electrocoat application conditions were voltage set point of 200V, a ramp time of 30 s, and a current density of −1.56 mA/cm2. The electrocoat was maintained at 90° F. Following deposition of the electrocoat, panels were baked in an electric oven (Despatch Model LFD-1-42) at 177° C. for 25 minutes.

Electrocoated panels were scribed with an X-shape. These were then submitted for the Daimler Chrysler Chipping Corrosion Test for 25 cycles. The test was conducted according to the procedure described in LP-463PB-52-01 Change B (published Nov. 11, 2002) from Daimler Chrysler Corporation. Loosely adhered paint and corrosion products were removed from the scribed area using Scotch 898 filament tape (available from 3M) after the completion of the testing. Four panels were run for each condition. The average scribe creep is displayed Table 7 below. Scribe creep refers to the area of paint loss around the scribe either through corrosion or disbondment (e.g., affected paint to affected paint).

Panels for each condition were also analyzed by X-ray fluorescence using an Axios Max-Advance X-Ray Fluorescence (XRF) spectrophotometer (PANanytical, Almelo, the Netherlands) to measure the Zr and Cu coatings weights. (A calibration curve was constructed and the XRF peak intensities for Zr and Cu correlated with coating weight (CW) determined through a hydrochloric acid stripping method using ICP-OES). The Zr/Cu ratio was then determined as the quotient of the Zr coating weight and the Cu coating weight. These results are reported in Table 7.

TABLE 7 Coating Weight and Chrysler Scab Corrosion Testing for Example 1 Zirconium Copper Avg. Immersion Coating Coating Scribe Condition Pretreatment Application Time Weight Weight Zr/Cu Creep Code Composition of Current (seconds) (mg/m²) (mg/m²) Ratio (mm) Comparison 1A PT A No 120 46 22 2.0 5.9 Control Process 1B PT B No 120 32 7 4.6 6.5 X: Equal Zr/Cu ratio 1C PT C No 480 100 61 1.6 5.8 Y: Equal Zr CW 1D PT C No 900 146 64 2.3 8.4 Z: Equal Zr CW 1E PT C Yes 60 67 14 4.8 3.3 X: Equal Zr/Cu ratio 1F PT C Yes 120 106 20 5.3 2.8 Y: Equal Zr CW 1G PT D Yes 120 144 7 20.6 2.8 Z: Equal Zr CW

Results: Application of current to a pretreatment bath increased the coating weight of Zr on a panel compared to a pretreatment bath without current. For pretreatment baths containing 35 ppm Cu, Table 7 shows panels treated according to Treatment Method A in Pretreatment Bath A with no current had 46 mg/m2 (Condition Code 1A) while panels treated according to Treatment Method B in Pretreatment Bath C had 106 mg/m2 Zr deposited (Condition Code 1F). For pretreatment baths containing 5 ppm Cu, Table 7 shows panels treated according to Treatment Method A in Pretreatment Bath B with no current had 32 mg/m² Zr deposited (Condition Code 1B) while panels treated according to Treatment Method B had 144 mg/m² Zr deposited (Condition Code 1G). The Zr deposition amount was increased by 2.3× at the higher copper level and 4.5× at the lower copper level. Without wishing to be bound by theory, the increase of a (Zr) deposition amount through flow of an electrical charge from the substrate into the pretreatment bath demonstrates an increased rate of hydroxide formation from the electrochemical splitting of water. The increased hydroxide formation enhances the formation of Zr oxide and Zr hydroxide at the substrate/pretreatment bath interface. Surprisingly, the rate of copper deposition is generally unaffected by the application of cationic (reducing) deposition conditions when comparing Condition Code 1A to Condition Code 1F and comparing Condition Code 1B to Condition Code 1G. One would expect the rate of copper deposition would increase under cathodic conditions since an excess of electrons are present that could reduce the Cu(II) in solution to either Cu(0) or Cu(I), both which can deposit onto the steel substrate. The results indicate that the amount of Cu deposition depends only on the concentration of copper with no effect from a presence of a cathodic current; that is, higher bath levels increase the copper coating weight in the pretreatment film. Additionally, the scribe creep results reported in Table 7 show that the application of current improves corrosion resistance on steel in cyclic testing as both current assisted deposition conditions are better than the corresponding spontaneously deposited film.

A comparison of similar Zr/Cu ratios can also be drawn among Condition Codes 1B, 1E, and 1F. In all three cases, the Zr/Cu ratio is roughly five to one. Under spontaneous deposition conditions (Condition Code 1B), corrosion resistance is worse than for the current assisted pretreatment condition (Condition Code 1E or Condition Code 1F). Condition Code 1E has the further advantage of reducing the time of deposition (60 second immersion time) while still providing comparable corrosion results to Condition Code 1F (120 second immersion time). Given that most industrially applied pretreatments are a time-constrained process, the application of current provides the flexibility in allowing the deposition of sufficient pretreatment to ensure acceptable corrosion resistance.

Two comparisons at equal coating weights of Zr can be drawn between (i) Condition Code 1C and Condition Code 1F and (ii) Condition Code 1D and Condition Code 1G. In the former case (1C/1F), approximately 100 mg/m² of Zr is deposited and in the latter case (1D/1G) roughly 140 mg/m² Zr is deposited. In both cases, the current assisted deposited condition resulted in less deposited Cu and improved corrosion protection. Without wishing to be bound by theory, the improved corrosion protection of current assisted pretreatment deposition seen in comparisons (i) and (ii) may be attributed to the lowering of copper incorporation into the film. When the Zr coating weight in the film is increased using a spontaneous deposition method, corrosion performance suffers (Condition Code 1C (100 mg/m² of Zr, 5.8 mm average scribe creep) vs. Condition Code 1D (146 mg/m2 of Zr, 8.4 mm average scribe creep)). This same effect is not observed in the pretreatment film generated under current assisted conditions; corrosion performance is equal for Condition Code 1F (106 mg/m² of Zr, 2.8 mm average scribe creep) and Condition Code 1G (144 mg/m2 of Zr, 2.8 mm average scribe creep). The divergence in corrosion resistance depending on the deposition mechanism (spontaneous vs. current assisted) suggests that spontaneously deposited thicker films are under higher inherent stress or porosity since the corrosion performance suffers. Moreover, this suggests that Zr pretreatment deposited under a cathodic bias are inherently lowers the film stress or these films are more compact at a given coating weight when compared to those spontaneously deposited.

Example 2. The Impact of Current Density on Zr/Cu Ratio

Introduction: Increasing the current density magnitude will increase the rate of water hydrolysis and in turn increase the concentration of hydroxide at the substrate/solution interface. In principle, deposition of zirconium oxide pretreatment under higher current densities will increase the rate of Zr precipitation resulting from larger concentration of hydroxide.

Preparation of PT Bath E (PT E): PT Bath E was prepared in a manner analogous to PT Bath A by the addition 18.9 liters of deionized (DI) water to an empty five-gallon plastic bucket. To the DI water was added hexafluorozirconic acid and copper solution. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively. Table 8 shows the pretreatment bath parameters for PT Bath E. A fresh 30-mL aliquot of solution of PT Bath E was used for each condition set forth in Table 10 below.

TABLE 8 Group IVB Pretreatment Bath Parameters for Example 2 Pretreatment Free Bath Code Zr (ppm) Cu (ppm) Fluoride (ppm) pH PT E 200 35 90 4.8

Alkaline Cleaner II (AC II): A rectangular stainless-steel tank with a total volume of 37 gallons, equipped with spray nozzles, was filled with 10 gallons of deionized water. To this was added 500 mL of Chemkleen SP1 (an alkaline cleaner available from PPG Industries, Inc.) and 50 mL of Chemkleen 185ALP (a blended surfactant additive available from PPG Industries, Inc.). Alkaline cleaner II was used for all conditions in Example 2.

Cold rolled steel (CRS) test panels (70 mm×150 mm×0.8 mm, Item #26920, audit grade, cut only, unpolished) were obtained from ACT Test Panel Technologies (Hillsdale, Mich.). CRS panels were coated using Treatment Methods D or E.

Panel pretreatment was conducted with or without cathodic bias using a pretreatment apparatus illustrated in FIG. 2 . Referring to FIG. 2 , pretreatment apparatus 200 includes anode 210 of a stainless-steel plate and substrate 220 of a cold rolled steel (CRS) plate which were separated by a polytetrafluoroethylene (PTFE) gasket 230. The panels were secured on the gasket using black binder clips (not shown). Deposition was conducted for thirty seconds in all cases.

The procedures for Treatment Method D and E are outlined in Tables 9 and 10 below. For panels treated according to Treatment Method D, panels (substrate 220) were spray cleaned and degreased for 120 seconds at 10-15 psi in alkaline cleaner IV (125° F.) using Vee-jet nozzles and were then rinsed by immersing in a deionized water bath (75° F.) for 30 seconds followed by a deionized water spray rinse using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (available from Home Depot) for 30 seconds. The apparatus described in FIG. 2 was then assembled and 30 mL of PT Bath E was added to the empty space. Exposure to the solution continued for 30 seconds after which the assembly was taken apart. The CRS panel (substrate 220) was rinsed by a deionized water spray rinse using the using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (75° F.) for 30 seconds, and dried with hot air (140° F.) for 120 seconds using a Hi-Velocity handheld blow-dryer made by Oster® (model number 078302-300-000) on high-setting.

For panels (substrate 220) treated according to Treatment Method E, panels were cleaned in the same manner as in Treatment Method D. Panel exposure to the pretreatment solution occurred in the same manner except current was applied for all of the conditions for Treatment Method E. The specific current densities are displayed Table 11. After pretreatment, the rinsing and drying sequence for Treatment Method E was identical to Treatment Method D.

TABLE 9 Treatment Method D Step 1D Alkaline cleaner (120 seconds, 125° F., spray application) Step 2D Deionized water rinse (30 seconds, 75° F., immersion application) Step 3D Deionized water rinse (30 seconds, 75° F., spray application) Step 4D Assemble coating apparatus Step 5D Zirconium Pretreatment (30 seconds exposure at 80° F., no cathodic bias) Step 6D Disassemble coating apparatus Step 7D Deionized water rinse (30 seconds, 75° F., spray application) Step 8D Hot Air Dry (120 seconds, 140° F.)

TABLE 10 Treatment Method E Step 1E Alkaline cleaner (120 seconds, 125° F., immersion application) Step 2E Deionized water rinse (30 seconds, 75° F., immersion application) Step 3E Deionized water rinse (30 seconds, 75° F., spray application) Step 4E Assemble coating apparatus Step 5E Zirconium Pretreatment (30 seconds exposure at 80° F., cathodic bias with variable current density) Step 6E Disassemble coating apparatus Step 7E Deionized water rinse (30 seconds, 75° F., spray application) Step 8E Hot Air Dry (120 seconds, 140° F.)

TABLE 11 Treatment conditions for Example 2 Current Condition Cleaner Pretreatment Application Density Immersion Time Treatment Code Bath Composition of Current (mA/cm²) (seconds) Method 2A AC II PTE No — 30 Method D 2B AC II PTE Yes −0.1 30 Method E 2C AC II PTE Yes −0.3 30 Method E 2D AC II PTE Yes −0.6 30 Method E 2E AC II PTE Yes −1.0 30 Method E 2F AC II PTE Yes −2.5 30 Method E 2G AC II PTE Yes −5.0 30 Method E 2H AC II PTE Yes −10.0 30 Method E 2I AC II PTE Yes −15.0 30 Method E

Panels (substrate 220) for each condition were also analyzed by a stripping method. A sample of pretreated panel was cut (6 cm×6 cm). The sample was exposed to 25 mL of 6 N hydrochloric acid for 5 minutes to dissolve the pretreatment layer. The solution was submitted for ICP-OES and the concentrations of Cu and Zr were measured. These were converted into a coating weight (milligrams per square meter) for each condition. The coating weight results appear in Table 12. The Zr/Cu ratio was then determined by taking the quotient of the Zr coating weight and the copper coating weight. These results are also reported in Table 12.

TABLE 12 Coating Weight and Zr/Cu Ratio for Example 2 Condition Application Current Zr Cu Code of Current Density (mA/cm²) CW CW Zr/Cu 2A No — 19 18 1.0 2B Yes −0.1 23 15 1.5 2C Yes −0.3 29 11 2.6 2D Yes −0.6 35 8 4.7 2E Yes −1.0 30 15 2.0 2F Yes −2.5 30 15 2.0 2G Yes −5.0 23 15 1.5 2H Yes −10.0 15 6 2.5 2I Yes −15.0 11 6 2.0

Results: Current density changes both the rate of Zr deposition and the Zr/Cu ratio of a pretreatment coating. FIG. 3 is a graph illustrating the impact of current density on zirconium deposition according to the method described in Example 2 with “Zr CW” representing the zirconium coating weight. FIG. 4 is a graph illustrating the impact of current density on zirconium/copper deposition according to the method described in Example 2 with “Zr CW/Cu CW” representing the quotient of the zirconium coating weight and the copper coating weight, both expressed in milligrams per square meter. Despite the fact that high current densities increase the rate of water hydrolysis, there is an optimal value for Zr deposition. As current density changes from 0 to −0.6 mA/cm², the rate of Zr deposition increased. However, the rate of Zr deposition decreased going from −1.0 to −15 mA/cm². A similar trend was observed for the Zr/Cu ratio.

When an electric field is applied to the two panels, the species in solution will migrate based on their surface charge. Species in solution that have a positive charge will flow toward the cathode whereas species with a negative charge will migrate toward the anode. At the surface of each electrode a double layer is formed which will control these species that will migrate toward that electrode. As current density is increased, the rate of Zr deposition diminishes. Without wishing to be bound by theory, the results of Example 2 imply that the Zr species in solution carry a negative charge and a strength of a double layer at the substrate/bath interface is reducing the efficiency of Zr deposition at the cathode. Moreover, the negative surface charge of Zr species in solution will preferentially be attracted to the positively charged anode. Thus, current density must be balanced to allow efficient deposition while overcoming the electric field assisted migration of the Zr species in solution.

Example 3. Effect of Applying a Current to Pretreatment Bath of Various Zr/Electropositive Metal Ratios Vs No Applied Current

Preparation of PT Bath F (PT F): PT Bath F was prepared by the addition 4500 milliliters of deionized (DI) water to an empty two-gallon plastic bucket. To the DI water was added potassium hexafluorozirconate. Separately, 3026 milliliters of deionized water was added to an empty one-gallon plastic bucket. To the DI water was added chromium (III) potassium sulfate. With a magnetic stir bar added to each container, the solutions were stirred at 300 RPM on a magnetic stir plate until the zirconium and chromium were dissolved. The solutions were blended and the pH was adjusted by using a dilute sulfuric acid solution.

Preparation of PT Bath G (PT G): PT Bath G was prepared in a manner analogous to PT Bath A by the addition 896 milliliters of deionized (DI) water to an empty half-gallon plastic bucket. To the DI water was added potassium hexafluorozirconate. Separately, 600 milliliters of deionized water was added to an empty one-quart plastic bucket. To the DI water was added chromium (III) potassium sulfate with the final concentration of chromium in the pretreatment bath being less than in PT Bath F. With a magnetic stir bar added to each container, the solutions were stirred at 300 RPM on a magnetic stir plate until the zirconium and chromium were dissolved. The Zr and Cr solutions were blended and the pH was adjusted by using a dilute sulfuric acid solution.

Preparation of PT Bath H (PT H): PT Bath H was prepared in a manner analogous to PT Bath A by the addition 896 milliliters of deionized (DI) water to an empty half-gallon plastic bucket. To the DI water was added potassium hexafluorozirconate. Separately, 600 milliliters of deionized water was added to an empty one-quart plastic bucket. To the DI water was added chromium (III) potassium sulfate with the final amount of chromium in the pretreatment bath being less than in PT Bath G. With a magnetic stir bar added to each container, the solutions were stirred at 300 RPM on a magnetic stir plate until the zirconium and chromium were dissolved. The Zr and Cr solutions were blended and the pH was adjusted by using a dilute sulfuric acid solution.

TABLE 13 Group IVB Pretreatment Bath Parameters for Example 3 Pretreatment Free Bath Code Zr (ppm) Cr (ppm) Fluoride (ppm) pH PT F 483 255 Not measured 3.12 PT G 483 120 7 3.25 PT H 483 97 7 3.27

Alkaline Cleaner III (AC III): AC III consisted of Bonderite C-AK 298 AERO (known as Ridoline 298), available from Henkel (Madison Heights, Mich.). AC III was prepared and maintained according to manufacturer's instructions. Alkaline cleaner III was used for all conditions in Example 3.

Deoxodizer Bath I (DB I): DB I consisted of Turco Deoxidizer 6/16, available from Henkel (Madison Heights, Mich.). DB I was prepared and maintained according to manufacturer's instructions. Deoxidizer I was used for all conditions in Example 3.

Aluminum test panels (2″×3″ unclad 2024T3 alloy/temper) were obtained from Bralco Metals (Wichita, Kans.). Aluminum panels were coated using one of two treatment methods, Treatment Methods F and G.

The procedures for Treatment Method F and G are outlined in Tables 14 and 15 below. For panels treated according to Treatment Method F, panels were immersion cleaned and degreased for 120 seconds in alkaline cleaner III (130° F.) and were then rinsed by immersing in a tap water bath (75° F.) for 60 seconds followed by a tap water squirt bottle rinse for 10 seconds. Panels were then immersed for 150 seconds in deoxidizer I (75° F.) and were then rinsed by immersing in a tap water bath (75° F.) for 60 seconds followed by a deionized squirt bottle rinse (75° F.) for 10 seconds. Panels were then immersed in PT Bath F, PT Bath G or PT Bath H for various times at 75° F. without the application of current. After deposition, the panels were rinsed by immersing in two sequential deionized water bath for 120 seconds each followed by a deionized squirt bottle rinse for 10 seconds. The panels were left to dry completely in ambient conditions.

For panels treated according to Treatment Method G, panels were cleaned and deoxidized the same manner as in Treatment Method F. The panels were then immersed for the specified time at 75° F. in the specified pretreatment bath. A DC supplied rectifier (Xantrex Model XFR600-2, Elkhart, Ind., or Sorensen XG 300-5.6, Ameteck, Berwyn, Pa.) was used to generate the constant current density listed in Table 16 for all of the conditions for Treatment Method G. The current assisted pretreatment application conditions were voltage set point of 10V, a ramp time of 0 s, and a pretreatment film thickness was controlled by time modulation with specifics defined in Table 16. The aluminum panel was the cathode and the anode were two stainless steel panels (each 1″ by 4″). After pretreatment and rinsing the drying for Treatment Method G was identical to Treatment Method F.

TABLE 14 Treatment Method F Step 1F Alkaline cleaner (120 seconds, 130° F., immersion application) Step 2F Tap water rinse (60 seconds, 75° F., immersion application) Step 3F Tap water rinse (10 seconds, 75° F., squirt bottle application) Step 4F Deoxidizer (150 seconds, 75° F., immersion application) Step 5F Tap water rinse (60 seconds, 75° F., immersion application) Step 6F Deionized water rinse (10 seconds, 75° F., squirt bottle application) Step 7F Zirconium Pretreatment (variable times, 75° F., immersion application) Step 8F Deionized water rinse (120 seconds, 75° F., immersion application) Step 9F Deionized water rinse (120 seconds, 75° F., immersion application) Step 10F Deionized water rinse (10 seconds, 75° F., squirt bottle application) Step 11F Air dry (ambient)

TABLE 15 Treatment Method G Step 1G Alkaline cleaner (120 seconds, 130° F., immersion application) Step 2G Tap water rinse (60 seconds, 75° F., immersion application) Step 3G Tap water rinse (10 seconds, 75° F., squirt bottle application) Step 4G Deoxidizer (150 seconds, 75° F., immersion application) Step 5G Tap water rinse (60 seconds, 75° F., immersion application) Step 6G Deionized water rinse (10 seconds, 75° F., squirt bottle application) Step 7G Zirconium Pretreatment (cathodic current, 75° F., immersion application) Step 8G Deionized water rinse (10 seconds, 75° F., squirt bottle application) Step 9G Air dry (ambient)

The pretreated panels were then submitted for unpainted neutral salt spray corrosion testing for 336 hours. After the completion of testing, panels were inspected with an unaided eye for corrosion sites (“pits”) across the face of the panel. Pits were counted as any corrosion event where white corrosion product was present. One panel was run for each condition. The number of pits displayed Table 16 below.

TABLE 16 Treatment conditions and Corrosion Results for Example 3 Current Immersion 14 Day Condition Pretreatment Application of Density Time Treatment Pitting Code Composition Current (mA/cm²) (seconds) Method Corrosion 3A PTF No — 120 Method F 18 3B PTG No — 120 Method F 27 3C PTG No — 240 Method F 15 3D PTG No — 360 Method F 33 3E PTG No — 600 Method F 12 3F PTH No — 120 Method F 13 3G PTH No — 240 Method F 41 3H PTH No — 360 Method F 34 3I PTH No — 600 Method F 45 3J PTF Yes −0.13 120 Method G 3 3K PTF Yes −0.67 120 Method G 0 3L PTF Yes −0.13 240 Method G 8 3M PTF Yes −0.33 240 Method G 0 3N PTF Yes −0.67 240 Method G 0 3O PTG Yes −0.32 120 Method G 2 3P PTG Yes −0.58 120 Method G 0 3Q PTG Yes −0.32 240 Method G 0 3R PTG Yes −0.58 240 Method G 0 3S PTH Yes −0.32 120 Method G 0 3T PTH Yes −0.58 120 Method G 0 3U PTH Yes −0.32 240 Method G 0 3V PTH Yes −0.58 240 Method G 1

Results: Application of current to a pretreatment bath improved unpainted neutral salt spray corrosion resistance compared to a pretreatment bath without current. For pretreatment baths containing a 1.9 Zr/Cr ratio (225 ppm Cr), Table 16 shows panels treated according to Treatment Method F in Pretreatment Bath F with no current (Condition Code 3A) had 18 pits while panels treated according to Treatment Method G in Pretreatment Bath F with current (Condition Codes 3J and 3K) had 3 pits and 0 pits. For pretreatment baths where the Zr/Cr ratio increases to 4/1, Table 16 shows panels treated according to Treatment Method F in Pretreatment Bath G with no current (Condition Code 3B) had 27 pits while panels treated according to Treatment Method G in Pretreatment Bath G with current (Condition Codes 3O and 3P) had 2 pits and 0 pits. For pretreatment bath where the Zr/Cr ratio increases to 5/1, Table 16 shows panels treated according to Treatment Method F in Pretreatment Bath H with no current (Condition Code 3B) had 13 pits while panels treated according to Treatment Method G in Pretreatment Bath G with current (Condition Codes 3Q and 3R) had 0 pits. When panels are treated according to Treatment Method F in Pretreatment Baths G or H without current at increased immersion times (Condition Codes 3C, 3D, 3E, 3G, 3H and 3I), the number of pits range from 12 to 25 compared to when panels are treated according to Treatment Method G in Pretreatment Baths G or H with current at increased immersion times (Condition Codes 3Q, 3R, 3U and 3V), the number of pits range from 0 to 1.

Example 4. The Effect of Immersion Time on Filiform Corrosion

Preparation of Zirconium Pretreatment Compositions: The pretreatment compositions for Example 4 were prepared in the same manner as described in Example 1 using the same chemicals. The exact bath parameters are recorded in Table 17.

Preparation of PT Bath I (PT I): PT Bath I was prepared in a manner analogous to PT Bath A by the addition 18.9 liters of water to an empty 5-gallon plastic bucket. To the DI water was added hexafluorozirconic acid, and the copper solution. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively.

TABLE 17 Pretreatment Bath Parameters for Example 4 Pretreatment Free Bath Code Zr (ppm) Cu (ppm) Fluoride (ppm) pH PT I 175 32 99 4.7

Alkaline Cleaner IV (AC IV): This cleaner was prepared in the same manner as AC I. A rectangular stainless steel tank with a total volume of 37 gallons, equipped with spray nozzles, was filled with 10 gallons of deionized water. To this was added 500 mL of Chemkleen 2010LP (a phosphate-free alkaline cleaner available from PPG Industries, Inc.) and 50 mL of Chemkleen 181ALP (a phosphate-free blended surfactant additive available from PPG Industries, Inc.). Alkaline cleaner IV was used in the preparation of panels for conditions tested in Example 4.

Aluminum panels (AA6022T43, 04X12X035 Cut Only, Unpolished, Item #APR39007) were purchased from ACT and cut to 10 cm×15 cm prior to pretreatment. When panels were prepared for filiform testing, the bottom portion of the aluminum panels was sanded. On aluminum panels, the bottom 7.5 centimeter of each panel was sanded with P320 grit paper available from 3M which was utilized on a 6″ random orbital palm sander available from ATD (Advanced Tool Design Model-ATD-2088). The sanding was utilized to help determine any difference in corrosion performance that may have been on sanded and unsanded parts of the metal. Sanding is used in the field as a means to increase the adhesion of subsequent paint surfaces and remove potential defects that can telegraph into upper layers of the coating stack, for example in the topcoat. Sanding will often expose intermetallic species, which will increase the propensity of substrates, especially aluminum, to experience accelerated corrosion. Thus, improved corrosion resistance on sanded aluminum is of great value to automotive manufacturers.

Panels were treated using either Treatment Method H or I, outlined in Tables 18 and 19 below. For panels treated according to Treatment Method H, panels were spray cleaned and degreased for 120 seconds at 10-15 psi in the alkaline cleaner (125° F.) using Vee-jet nozzles and rinsed with deionized water by immersing in a deionized water bath (75° F.) for 30 seconds followed by a deionized water spray rinse using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (available from Home Depot). All panels were immersed in PT I for 120 seconds (80° F.), rinsed by a deionized water spray rinse using the using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (75° F.) for 30 seconds, and dried with hot air (140° F.) for 120 seconds using a Hi-Velocity handheld blow-dryer made by Oster® (model number 078302-300-000) on high-setting.

For panels treated according to Treatment Method I, panels were cleaned, pretreated, and rinsed as in Method H, except that during the application of PT I, a cathodic current was applied to the panel. The current densities used during the pretreatment process are indicated in Table 20. Following the pretreatment and subsequent DI rinse, panels were then dried with hot air (140° F.) for 120 seconds using a Hi-Velocity handheld blow-dryer made by Oster® (model number 078302-300-000) on high-setting.

Coatings weights as determined by XRF as described in this application and are found in Table 22.

TABLE 18 Treatment Method H Step 1H Alkaline cleaner (120 seconds, 125° F., spray application) Step 2H Deionized water rinse (30 seconds, 75° F., immersion application) Step 3H Deionized water rinse (30 seconds, 75° F., spray application) Step 4H Zirconium Pretreatment (120 seconds, 80° F., immersion application) Step 5H Deionized water rinse (30 seconds, 75° F., spray application) Step 6H Hot Air Dry (120 seconds, 140° F.)

TABLE 19 Treatment Method I Step 1I Alkaline cleaner (120 seconds, 125° F., spray application) Step 2I Deionized water rinse (30 seconds, 75° F., immersion application) Step 3I Deionized water rinse (30 seconds, 75° F., spray application) Step 4I Zirconium Pretreatment (cathodic current, 120 seconds, 80° F., immersion application) Step 5I Deionized water rinse (30 seconds, 75° F., spray application) Step 6I Hot Air Dry (120 seconds, 140° F.)

TABLE 20 Treatment conditions for Example 4. PT Electro- Total Condition Cleaner Compo- Current deposition Immersion Code Bath sition Density Time Time 4A AC IV PT I N/A 0 s  30 s 4B AC IV PT I −0.30 mA/cm² 30 s   30 s 4C AC IV PT I N/A 0 s 120 s 4D AC IV PT I −0.30 mA/cm² 120 s  120 s 4E AC IV PT I N/A 0 s 300 s 4F AC IV PT I −0.30 mA/cm² 300 s  300 s

Following completion of Treatment Methods H or I, all panels were electrocoated with ED7000Z (a cathodic electrocoat with components commercially available from PPG) prepared by mixing E6433Z resin (6116.70 grams), E6434Z paste (1073.37 grams), and deionized water (4810.50 grams). The paint was ultrafiltered removing 25% of the material, which was replenished with fresh deionized water. This paint was applied in the same manner as described in the conditions for Example 1.

Electrocoated panels were subjected to filiform corrosion testing, modified EN3665. Electrocoated panels were scribed with a vertical line (3-4 inches). These panels were then exposed to hydrochloric acid vapor for one hour while being stored in a vertical position. After HCl vapor exposure, the panels were aged in a cabinet held at 80% humidity and 40° C. for 12 weeks on plastic racks. The corrosion results are shown in Table 21 below. Panels subjected to modified EN3665 were evaluated by measuring the average of the five longest filiform thread lengths, reported in mm, without removal of loosely adhered paint by external means (e.g.: blasting).

TABLE 21 Corrosion results on aluminum for Example 2. EN3665 - EN3665 - Applica- Copper Total Filiform Edge Condition tion of Level Immersion Thread Corrosion Code Current (ppm) Time Length (mm)^(A) Rating^(B) 4A No 32  30 s 4.1 5 4B Yes 32  30 s 2.7 3 4C No 32 120 s 3.0 3 4D Yes 32 120 s 1.8 2 4E No 32 300 s 3.1 3 4F Yes 32 300 s 2.6 3 ^(A)Minimal corrosion/filiform was observed on the unsanded area of the panel. The longest filiform threads were present on the sanded areas of the coated aluminum. ^(B)Edge corrosion was qualitatively determined with ratings from 1-5. A rating of 1 represented minimal edge filiform and 5 indicated served filiform formation at the edge.

TABLE 22 Coating composition on aluminum for Example 4 conditions. Copper Total Condition Application Level Immersion ZrCW Cu CW Zr/Cu Code of Current (PPm) Time (mg/m²) (mg/m²) Ratio 4A No 32  30 s 15 4 3.8 4B Yes 32  30 s 26 3 8.0 4C No 32 120 s 27 8 3.4 4D Yes 32 120 s 96 11 9.0 4E No 32 300 s 34 19 1.8 4F Yes 32 300 s 188 18 10.6

Results: Application of current reduced the formation of filiform corrosion at the scribe and at the edge of treated panels. The improvement in corrosion can be attributed to the increase in Zr CW/Cu CW ratio observed when comparing the passive and electrochemically assisted deposition processes. Reduction of copper deposition is very important on aluminum as high(er) levels of deposited Cu may reduce the corrosion resistance of pretreated and electrocoated panels.

Example 5: Improvement in Performance on Welded and Heat Affected Zones with Applied Current

Introduction: Welding is used as a way to join steel and other materials in the construction of automobiles and industrial construction. The high temperature used for welding can modify the steel crystal structure, which may change the reactivity of the material toward pretreatment. Additionally, the high heat, welding flux, and presence of oxygen often leads to the formation of thick iron/metal oxides on the joined areas. These areas are difficult to pretreat and often require the application of an acidic etch to remove the weld scale. Zinc phosphate, having a pH around 3, is more effective at removing the weld scale when compared to Group IVB pretreatment which tend to have a pH greater than 4. It would be ideal to modify the application process of Group IVB to deposit pretreatment of the weld scale.

Preparation of Zirconium Pretreatment Compositions: The pretreatment compositions for Example 5 were prepared in the same manner as described in Example 1 using the same chemicals. The exact bath parameters are recorded in Table 23.

Preparation of PT Bath J (PT J): PT Bath I was prepared in a manner analogous to PT Bath A by the addition 3.8 liters of water to an empty one-gallon plastic tube. To the DI water was added hexafluorozirconic acid, and the copper solution. The pH and free fluoride of the bath was adjusted by using Chemfil Buffer and Chemfos AFL, respectively.

Preparation of Zirconium Control Bath (PT ZC): A one-gallon solution of ZircoBond II (a zirconium-containing pretreatment composition commercially available from PPG Industries, Inc.) was prepared according to the manufacturer's instructions. The bath had a pH of 4.7 and contained 175 ppm of zirconium, 30 ppm of copper, 75 ppm molybdenum, and 85 ppm of free fluoride.

Activating Rinse for Zinc Phosphate: Versabond Rinse Conditioner (Zn phosphate-based material) was obtained from PPG Industries. The activating rinse bath was prepared by adding 1.1 grams of Versabond RC concentrate per liter of deionized water, to give an activator bath with a zinc phosphate concentration of 0.5 grams per liter.

Preparation of Zinc Phosphate Control Bath (PT ZnP): A Chemfos 700AL (CF 700AL) zinc phosphate pretreatment bath was produced according to manufacturer's instructions by filling a five-gallon vessel approximately three-fourths full with deionized water. To this was added 700 ml of Chemfos 700A, 1.5 ml Chemfos FE, 51 ml Chemfos AFL, and 350 ml of Chemfos 700B (all commercially available from PPG). To this was added 28.6 g zinc nitrate hexahydrate and 2.5 grams of sodium nitrite (both available from Fischer Scientific), and the free acid of the bath was operated at 0.7-0.8 points of free acid, 15-19 points of total acid, and 2.2-2.7 gas points (mL). To obtain the correct amounts of free and total acid, Chemfos 700B was utilized to adjust according to product data sheet. The temperature of the bath was 125° F. and panels were immersed in the bath for 2 minutes.

TABLE 23 Group IVB Pretreatment Bath Parameters for Example 5 Pretreatment Free Bath Code Zr (ppm) Cu (ppm) Fluoride (ppm) pH PT J 175 30 100 4.7 PT ZC 175 30 70 4.6

Alkaline Cleaner V (AC V): A rectangular stainless steel tank with a total volume of 37 gallons, equipped with spray nozzles, was filled with 10 gallons of deionized water. To this was added 500 mL of Chemkleen 2010LP (a phosphate-free alkaline cleaner available from PPG Industries, Inc.) and 50 mL of Chemkleen 181ALP (a phosphate-free blended surfactant additive available from PPG Industries, Inc.). Alkaline cleaner V was used for all conditions in example 5.

Alkaline Cleaner VI (AC VI): A five-gallon bucket was filled with 5 gallons of deionized water. To this was added 250 mL of Chemkleen 2010LP (a phosphate-free alkaline cleaner available from PPG Industries, Inc.) and 25 mL of Chemkleen 181ALP (a phosphate-free blended surfactant additive available from PPG Industries, Inc.). An immersion heater was placed into the bucket and the alkaline solution was heated to 125° F. The immersion heater was set to the “high” setting. Alkaline cleaner VI was used after AC V for all conditions in example 5.

Spangler panels such as illustrated in FIG. 5 were obtained from Laser Precision (Caterpillar Part No. 381-0134; 24.95×9.95 cm). Substrate 300 is composed of two cold-rolled steel (CRS) panels (flat or backing panel 310 and inset panel 320) welded together with four spot welds 330 and one seam weld 340. Galvanized nut 350 is welded to flat panel 310. Additionally, there are three laser cut holes (two circles 360 and one rectangle 370). The joining methods of flat panel 310 and inset panel 320 are completed using high temperature which will change the crystal structure of the steel resulting in “heat affected zones”. Panels were treated with Treatment Method J for current-assisted deposition, Treatment Method K for Zircobond II comparative, and Treatment Method L for zinc phosphate controls and their respective coatings were evaluated.

Panels were treated using Treatment Method J, K or L, which are outlined in Tables 24, 25, and 26 below. For panels treated according to Treatment Method J, panels were spray cleaned and degreased for 60 seconds at 10-15 psi in alkaline cleaner V (125° F.) using Vee-jet nozzles and then immersed in alkaline cleaner VI for 120 seconds under high agitation at 125° F. The panels were then rinsed by immersing in a deionized water bath (75° F.) for 30 seconds followed by a deionized water spray rinse using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (available from Home Depot) for 30 seconds. Panels were then immersed in PT J for 120 seconds (80° F.) with catholic current applied. After deposition, the panels were rinsed by a deionized water spray rinse using the using a Melnor Rear-Trigger 7-Pattern nozzle set to shower mode (75° F.) for 30 seconds, and dried with hot air (140° F.) for 120 seconds using a Hi-Velocity handheld blow-dryer made by Oster® (model number 078302-300-000) on high-setting.

For panels treated according to Treatment Method K (zirconium control), panels were cleaned the same manner as in Treatment Method J. The panels were then immersed into the PT ZC for 120 seconds at 80° F. (no applied current). After pretreatment, the rinsing sequence for Treatment Method K was identical to Treatment Method J.

For panels treated according to Treatment Method L (zinc phosphate control), panels were cleaned the same manner as in Treatment Method J. The panels were then immersed into the activator for 60 seconds at ambient temperature and then transferred to the zinc phosphate bath (PT ZnP) for 120 seconds at 125° F. After pretreatment, the rinsing sequence for Treatment Method L was identical to Treatment Method J.

TABLE 24 Treatment Method J Step 1J Alkaline cleaner (60 seconds, 125° F., spray application) Step 2J Alkaline cleaner (120 seconds, 125° F., immersion application) Step 3J Deionized water rinse (30 seconds, 75° F., immersion application) Step 4J Deionized water rinse (30 seconds, 75° F., spray application) Step 5J Zirconium Pretreatment (cathodic current, 120 seconds, 80° F., immersion application) Step 6J Deionized water rinse (30 seconds, 75° F., spray application) Step 7J Hot Air Dry (120 seconds, 140° F.)

TABLE 25 Treatment Method K Step 1K Alkaline cleaner (60 seconds, 125° F., spray application) Step 2K Alkaline cleaner (120 seconds, 125° F., immersion application) Step 3K Deionized water rinse (30 seconds, 75° F., immersion application) Step 4K Deionized water rinse (30 seconds, 75° F., spray application) Step 5K Zirconium Control Pretreatment (PT ZC, 120 seconds, 80° F., immersion application) Step 6K Deionized water rinse (30 seconds, 75° F., spray application) Step 7K Hot Air Dry (120 seconds, 140° F.)

TABLE 26 Treatment Method L Step 1L Alkaline cleaner (60 seconds, 125° F., spray application) Step 2L Alkaline cleaner (120 seconds, 125° F., immersion application) Step 3L Deionized water rinse (30 seconds, 75° F., immersion application) Step 4L Deionized water rinse (30 seconds, 75° F., spray application) Step 5L Rinse Conditioner (60 seconds, 75° F., immersion application) Step 6L Zinc phosphate Control Pretreatment (PT ZnP, 120 seconds, 125° F., immersion application) Step 7L Deionized water rinse (30 seconds, 75° F., spray application) Step 8L Hot Air Dry (120 seconds, 140° F.)

TABLE 27 Treatment conditions for Example 5. Cleaner Pretreatment Application Current Density Treatment Condition Bath Composition of Current (mA/cm²) Method 5A AC V/AC VI PT J Yes −0.3 mA/cm² Method J 5B AC V/AC VI PT J Yes −0.6 mA/cm² Method J 5Z AC V/AC VI PT ZC No N/A Method K 5P AC V/AC VI PT ZnP No N/A Method L

Following completion of Treatment Methods J, K, or L, all panels were electrocoated with ED7000Z (a cathodic electrocoat with components commercially available from PPG) prepared by mixing E6433Z resin, E6434Z paste, and deionized water as described above. The paint was ultrafiltered removing 25% of the material, which was replenished with fresh deionized water. The electrocoat was applied in the manner described above with a target film thickness of 0.6±0.1 mils both flat and inset panels. The DFT was controlled by changing the amount of charge (coulombs) that passed through the panels. Following deposition of the electrocoat, panels were baked in an oven (Despatch Model LFD-1-42) at 177° C. for 25 minutes.

Electrocoated panels were scribed on both the flat panel and the inset welded panel. Panels were submitted to GMW14872 testing for 40 cycles. The conditions are described in Table 28. After corrosion testing, panels were subjected to media blasting (MB-2, an irregular granular plastic particle with a Moh's hardness of 3.5 and size range of 0.58 mm-0.84 mm available from Maxi-Blast, Inc., South Bend, Ind.) using an In Line Conveyor System IL-885 Sandblaster (incoming air pressure of 85 psi, Empire Abrasive Equipment Company, model information: IL885-M9655) after corrosion testing to remove loosely adhered paint and corrosion products. One panel was run each condition for each corrosion test. The average scribe creep for both the flat and inset panels are shown in Tables 29. Scribe creep refers to the area of paint loss around the scribe either through corrosion or disbondment (e.g.: affected paint to affected paint).

TABLE 28 Corrosion tests used in Example 5 for electrocoated Spangler panels. Corrosion Test Corrosion Test Substrate Scribe Length Type GMW14872 Spangler (steel) Vertical Line 40 Cycles Blister

TABLE 29 Corrosion results from GM14872 corrosion testing for Example 5. Flat Inset Panel—Avg. Panel—Avg. Current Cu Scribe Scribe Pretreatment Application Density Level Creep Creep Condition Composition of Current (mA/cm²) (ppm) (mm) (mm) 5A PT J Yes −0.30 30 1.7 2.4 mA/cm² 5B PT J Yes −0.60 30 1.6 3.6 mA/cm² 5Z PT ZC No N/A 30 2.3 5.5 5P PT ZnP No N/A N/A 3.2 5.6

Results: Application of current improves Group IVB deposition on unreactive heat affected zones. A comparison of standard pretreatments (zinc phosphate and Group IVB control) demonstrate the challenge of treating heat affected zones (with relatively large scribe creeps on the inset panel). Using −0.3 or −0.6 mA/cm² provided corrosion results on the both flat panel and the welded inset panel that were superior to the zinc phosphate control. These results are significant because they provide an improvement in corrosion protection for Group IVB which is superior to zinc phosphate despite the higher pH (4.7) which will not remove a significant amount of the weld scale. 

1. A method for treating a substrate comprising: contacting a substrate with a pretreatment composition comprising a Group IVB metal and an electropositive metal; and passing an electric current between an anode and the substrate serving as a cathode to deposit a coating from the pretreatment composition on the substrate.
 2. The method of claim 1, wherein the Group IVB metal comprises zirconium.
 3. The method of claim 1, wherein the electropositive metal comprises copper.
 4. The method of claim 1, wherein the electropositive metal comprises trivalent chromium.
 5. The method of claim 1, wherein the pretreatment composition further comprises a fluoride ion.
 6. The method of claim 1, wherein the Group IVB metal is in the range of 4 to 40 times by weight an amount of the electropositive metal.
 7. The method of claim 1, wherein the Group IVB metal comprises zirconium and the electropositive metal comprises copper.
 8. The method of claim 7, wherein the coating comprises a weight ratio of the Group IVB metal to the electropositive metal greater than 4:1.
 9. The method of claim 1, wherein the electric current comprises a current density of |−1| milliamp per square centimeters (mA/cm²) or less.
 10. The method of claim 1, wherein the current density comprises a current density of |−0.6| milliamp per square centimeters (mA/cm²) or less.
 11. The method of claim 1, wherein the substrate comprises a steel.
 12. The method of claim 1, where the substrate comprises aluminum.
 13. The method of claim 1, wherein the substrate comprises a portion of a vehicle.
 14. The method of claim 1, wherein the coating has a property that provides corrosion resistance to the substrate.
 15. The method of claim 14, wherein the corrosion resistance is filiform corrosion resistance.
 16. A substrate treated by the method of claim
 1. 17.-44. (canceled)
 45. The substrate of claim 16, wherein the substrate is an automotive component.
 46. The substrate of claim 45, wherein the automotive component comprises steel.
 45. The substrate of claim 16, wherein the substrate comprises a vehicle, a vehicle body, a vehicle frame, a vehicle component or combinations thereof.
 46. The substrate of claim 45, wherein the vehicle comprises an aircraft or a body, frame or component thereof.
 47. The substrate of claim 46, wherein the substrate comprises aluminum, an aluminum alloy or combinations thereof.
 48. The substrate of claim 45, wherein the vehicle comprises a land vehicle or a body, frame or component thereof.
 49. The substrate of claim 48, wherein the substrate comprises steel. 